Signal-to-noise Ratio Degradation Research Articles

On the performance of OFDM-IM systems in the presence of CFO effects

This study presents a comprehensive analysis of the performance degradation effects of carrier frequency offset (CFO) on orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems operating over frequency-selective multipath fading channels. CFO is an impairing factor that degrades the signal-to-noise ratio (SNR) through signal attenuation and inter-carrier interference (ICI). We derive a closed-form expression to quantify the SNR degradation under CFO for OFDM-IM systems. Additionally, we formulate a very tight upper bound for the bit error rate (BER), accounting for index modulation errors, CFO distortion, and multipath fading.The presented analytical formulations capture the unique characteristics of OFDM-IM systems and facilitate precise performance evaluation. The findings yield valuable insights into mitigating CFO-induced BER degradation through appropriate system parameter selection and CFO compensation techniques. Moreover, this investigation makes significant contributions towards designing reliable OFDM-IM communication links resilient to the combined effects of index modulation, frequency offsets, and dispersive channel conditions.

Optimizing elastic optical networks quality of transmission with an empirical optical amplifier gain saturation model

In this paper, we revisit the problem of adjusting transceiver power, amplifier gain, and nodal gain in optical-bypass-enabled networks, taking into account an empirical model of erbium-doped fiber amplifier (EDFA) gain saturation. We assume that network demands have been routed via the shortest possible paths. A heuristic algorithm, which estimates the degradation of the signal-to-noise ratio (SNR) for each demand, is used to assign the modulation level and spectrum slots to the routed demands. Our optimization process aims to maximize the minimum SNR margins of demands, by adjusting EDFA small-signal gain, variable optical attenuator (VOA) attenuation, and transceiver power. Constraints and impairments imposed by the physical-layer include EDFA and VOA gain limits, transceiver power limits, receiver sensitivity, insertion loss of optical switch input ports, EDFA gain saturation, EDFA noise, and fiber non-linear interference. These are modeled using the Gaussian noise model. The proposed optimization problem is formulated as a geometric programming problem and then converted into an equivalent convex problem.Numerical results suggest that in the optimal solution of our optimization, all demands are served with typically low bit error rates (BER) (<10−4). We calculate the operational gains of the EDFA to set the spans to full compensation whenever possible. Pre-amplifiers and line amplifiers do not experience gain saturation due to relatively small input powers, while approximately 10% of boosters undergo more than a 1 dB gain reduction due to high input powers. We observe that overlooking the effect of EDFA gain saturation and physical-layer-imposed constraints such as nodal gain limits or transceiver power limits during network optimization leads to a considerable number of blocked demands due to SNR degradation or high BER (>10−3).

Spectral Engineering for Optimal Signal Performance in the Microwave SQUID Multiplexer

AbstractWe describe a technique to optimize the dynamic performance of microwave SQUID multiplexer (µMUX)-based systems. These systems proved to be adequate for reading out multiple cryogenic detectors simultaneously. However, the requirement for denser detector arrays to increase the sensitivity of scientific experiments makes its design a challenge. When modifying the readout power, there is a trade-off between decreasing the signal-to-noise ratio (SNR) and boosting the nonlinearities of the active devices. The latter is characterized by the spurious free dynamic range (SFDR) parameter and manifests as an increment in the intermodulation products and harmonics power. We estimate the optimal spectral location of the SQUID signal containing the detector information for different channels. Through the technique, what we refer to as Spectral Engineering, it is possible to minimize the SNR degradation while maximizing the SFDR of the detector signal, thus, overcoming the trade-off.

A Systematic Method for Scaling Coefficients of the Continuous-Time Low-Pass ΣΔ Modulator Using a Simulink-Based Toolbox

The sigma-delta modulator (SDM) is one of the well-established data converter architectures. It is well-known for achieving a high signal-to-noise ratio (SNR). In the SDM, the integrators in the loop filter could suffer from overloading if the signal swing exceeds its maximum level, which leads to performance and SNR degradation. Thus, scaling the system coefficients is needed, such that there is no overloading for the integrators. In this work, we present a systematic general method that could be used for scaling the signal swings in the continuous-time low-pass sigma-delta modulator (SDM). The proposed method can be applied to any continuous-time low-pass SDM architecture, and it includes the scaling of all the possible combinations of the system coefficients. Moreover, an open-source Simulink-based toolbox that includes the systematic method is presented. This toolbox could help the designer to execute the scaling process and the simulations in an efficient way. In addition to that, a design example is discussed to illustrate the proposed method, wherein the presented toolbox is used for simulations, and the simulation results are shown.

Signal-to-noise ratio degradation analysis for optoelectronic feedback-based chaotic optical communication systems.

Chaotic optical communication encrypts transmitted signals through physical noise; this ensures high security while causing a certain decrease in the signal-to-noise ratio (SNR). Thus, it is necessary to analyze the SNR degradation of decrypted signals after chaotic encryption and the minimum requirements for the SNR of the fiber channel to meet the required bit error rate (BER) performance. Accordingly, an SNR model of decrypted signals for optoelectronic feedback-based chaotic optical communication systems is proposed. Under different channel SNRs, the SNR degradation of 40 Gbit/s phase chaos and intensity chaos models is investigated by simulation and experiment, respectively, with a 15 GHz wideband chaotic carrier. Comparing decrypted signals with original signals, the simulation results show that there is a 2.9 dB SNR degradation for both intensity chaos and phase chaos. Further, in experiments, SNR degradation from 4.5 dB to 5.6 dB, with various channel SNRs for intensity chaos, is analyzed, while there is an SNR degradation from 7.1 dB to 8.3 dB for phase chaos. The simulation and experimental results provide guidance for long-distance transmission chaotic optical communication systems.

First Observations With a GNSS Antenna to Radio Telescope Interferometer

AbstractWe describe the design of a radio interferometer composed of a Global Navigation Satellite Systems (GNSS) antenna and a Very Long Baseline Interferometry radio telescope. Our eventual goal is to use this interferometer for geodetic applications including local tie measurements. The GNSS element of the interferometer uses a unique software‐defined receiving system and modified commercial geodetic‐quality GNSS antenna. We ran three observing sessions in 2022 between a 25 m radio telescope in Fort Davis, Texas (FD‐VLBA), a transportable GNSS antenna placed within 100 m, and a GNSS antenna placed at a distance of about 9 km. We have detected a strong interferometric response with a Signal‐to‐Noise Ratio (SNR) of over 1,000 from Global Positioning System and Galileo satellites. We also observed natural radio sources including Galactic supernova remnants and Active Galactic Nuclei located as far as one gigaparsec, thus extending the range of sources that can be referenced to a GNSS antenna by 18 orders of magnitude. These detections represent the first observations made with a GNSS antenna to radio telescope interferometer. We have developed a novel technique based on a Precise Point Positioning solution of the recorded GNSS signal that allows us to extend integration time at 1.5 GHz to at least 20 min without any noticeable SNR degradation when a rubidium frequency standard is used.

Study on channel prediction in IRS-assisted wireless communication systems

The use of intelligent reflecting surface (IRS) is being investigated for wireless communication in high frequency bands. By appropriately controlling the reflection coefficient of each IRS element, high quality communication can be achieved even in non-line-of-sight environment. The phase control of the IRS requires the determination of the optimal phase pattern based on the estimated channel, which is then fed back to the IRS through the control channel. To reduce channel estimation overhead, we propose a channel prediction method based on Gaussian process regression. We evaluate the proposed method performance on the points of signal-to-noise ratio (SNR) and confirm that the proposed approach can mitigate SNR degradation caused by terminal movement compared to the system without prediction.

Photonic compressive sampling of wideband sparse radio frequency signals with 1-bit quantization.

Photonic compressive sampling (PCS) is an effective method to recover wideband sparse radio frequency (RF) signals. However, the noisy and high-loss photonic link leads to signal-to-noise ratio (SNR) degradation of the RF signal to be tested, which limits the recovery performance of the PCS system. In this paper, a random demodulator-based PCS system with 1-bit quantization is proposed. The system consists of a photonic mixer, a low-pass filter, a 1-bit analog-to-digital converter (ADC), and a digital signal processor (DSP). The 1-bit quantized result is used to recover the spectra of the wideband sparse RF signal with the binary iterative hard thresholding (BIHT) algorithm, which can alleviate the negative impact of the SNR degradation caused by the photonic link. A full theoretical framework of the PCS system with 1-bit quantization is given. Simulation results show that the PCS system with 1-bit quantization can provide better recovery performance than the traditional PCS system under low SNR and stringent bit budget.

Experimental impact of power re-optimization in a mesh network

We experimentally observe the signal-to-noise ratio (SNR) degradation of previously established services induced by loading new services in a network, and we mitigate this degradation by periodic power re-optimization via two different strategies: (1) a static strategy based on end-of-life parameters and (2) a dynamic strategy based on real-time monitoring to the current state of the network. We use a mesh network testbed of four nodes and five links with commercial equipment only. We observe up to 3.4 dB SNR degradation on the previously established services due to the loading of new services. Then we demonstrate an improvement of up to 3.2 dB in the network margin achieved by applying our proposed power re-optimization strategy.

Challenges regarding MR compatibility of an MRgFUS robotic system

Numerous challenges are faced when employing Magnetic Resonance guided Focused Ultrasound (MRgFUS) hardware in the Magnetic Resonance Imaging (MRI) setting. The current study aimed to provide insights on this topic through a series of experiments performed in the framework of evaluating the MRI compatibility of an MRgFUS robotic device. All experiments were performed in a 1.5 T MRI scanner. The main metric for MRI compatibility assessment was the signal to noise ratio (SNR). Measurements were carried out in a tissue mimicking phantom and freshly excised pork tissue under various activation states of the system. In the effort to minimize magnetic interference and image distortion, various set-up parameters were examined. Significant SNR degradation and image distortion occurred when the FUS transducer was activated mainly owing to FUS-induced target and coil vibrations and was getting worse as the output power was increased. Proper design and stable positioning of the imaged phantom play a critical role in reducing these vibrations. Moreover, isolation of the phantom from the imaging coil was proven essential for avoiding FUS-induced vibrations from being transferred to the coil during sonication and resulted in a more than 3-fold increase in SNR. The use of a multi-channel coil increased the SNR by up to 50 % compared to a single-channel coil. Placement of the electronics outside the coil detection area increased the SNR by about 65 %. A similar SNR improvement was observed when the encoders' counting pulses were deactivated. Overall, this study raises awareness about major challenges regarding operation of an MRgFUS system in the MRI environment and proposes simple measures that could mitigate the impact of noise sources so that the monitoring value of MR imaging in FUS applications is not compromised.

A 2.03-mW CMOS Image Sensor With an Integrated Four-Stacked Charge-Recycling Driver for Image Signal Transmission

We propose a CMOS image sensor with a dedicated low-power imaging mode and low-power integrated transmitter. The proposed CMOS image sensor selectively operates in dual mode: a high-quality mode with a 1.5 V supply voltage of readout circuits to achieve a high signal-to-noise ratio (SNR), and a low-power mode with a 0.9 V supply voltage to support always-on imaging. To further reduce the power consumption in the low-power mode, a single-slope analog to digital converter (ADC) embeds a power cutoff scheme in the comparator and a two-step conversion with dual reference voltages. To alleviate the SNR degradation in the low-power mode, which inherently occurs from voltage scaling, a correlated multiple sampling technique that consumes negligible power overhead is implemented using the proposed window-counting scheme. To reduce the significant power consumption that occurs during image signal transmission, an integrated transmitter with four-stacked charge-recycling drivers is used so that four symbols are simultaneously transmitted with a shared supply voltage. A prototype CMOS image sensor with 680 × 520 pixels is fabricated using 110-nm CMOS image sensor technology. The fabricated CMOS image sensor consumes only 301 μW (at 15 fps) in the sensor core and 2.03 mW including the transmitter and phase locked loop (PLL) while generating low temporal random noise under 0.27 LSB with correlated multiple sampling.

Tensor-Based Reduced-Dimension MUSIC Method for Parameter Estimation in Monostatic FDA-MIMO Radar

Frequency diverse array (FDA) radar has attracted much attention due to the angle and range dependence of the beam pattern. Multiple-input-multiple-output (MIMO) radar has high degrees of freedom (DOF) and spatial resolution. The FDA-MIMO radar, a hybrid of FDA and MIMO radar, can be used for target parameter estimation. This paper investigates a tensor-based reduced-dimension multiple signal classification (MUSIC) method, which is used for target parameter estimation in the FDA-MIMO radar. The existing subspace methods deteriorate quickly in performance with small samples and a low signal-to-noise ratio (SNR). To deal with the deterioration difficulty, the sparse estimation method is then proposed. However, the sparse algorithm has high computation complexity and poor stability, making it difficult to apply in practice. Therefore, we use tensor to capture the multi-dimensional structure of the received signal, which can optimize the effectiveness and stability of parameter estimation, reduce computation complexity and overcome performance degradation in small samples or low SNR simultaneously. In our work, we first obtain the tensor-based subspace by the high-order-singular value decomposition (HOSVD) and establish a two-dimensional spectrum function. Then the Lagrange multiplier method is applied to realize a one-dimensional spectrum function, estimate the direction of arrival (DOA) and reduce computation complexity. The transmitting steering vector is obtained by the partial derivative of the Lagrange function, and automatic pairing of target parameters is then realized. Finally, the range can be obtained by using the least square method to process the phase of transmitting steering vector. Method analysis and simulation results prove the superiority and reliability of the proposed method.

Flexible Multi-Turn Multi-Gap Coaxial RF Coils: Design Concept and Implementation for Magnetic Resonance Imaging at 3 and 7 Tesla.

Magnetic resonance has become a backbone of medical imaging but suffers from inherently low sensitivity. This can be alleviated by improved radio frequency (RF) coils. Multi-turn multi-gap coaxial coils (MTMG-CCs) introduced in this work are flexible, form-fitting RF coils extending the concept of the single-turn single-gap CC by introducing multiple cable turns and/or gaps. It is demonstrated that this enables free choice of the coil diameter, and thus, optimizing it for the application to a certain anatomical site, while operating at the self-resonance frequency. An equivalent circuit for MTMG-CCs is modeled to predict their resonance frequency. Possible configurations regarding size, number of turns and gaps, and cable types for different B 0 field strengths are calculated. Standard copper wire loop coils (SCs) and flexible CCs made from commercial coaxial cable were fabricated as receive-only coils for 3 T and transmit/receive coils at 7 T with diameters between 4 and 15 cm. Electromagnetic simulations are used to investigate the currents on MTMG-CCs, and demonstrate comparable specific absorption rate of 7 T CCs and SCs. Signal-to-noise ratio (SNR), transmit efficiency, and active detuning performance of CCs were compared in bench tests and MR experiments. For the form-fitted receive-only CCs at 3 T no significant SNR degradation was found as compared to flat SCs on a balloon phantom. Form-fitted transmit/receive CCs at 7 T showed higher transmit efficiency and SNR. MTMG-CCs can be sized to optimize sensitivity, are flexible and lightweight, and could therefore enable the fabrication of wearable coils with improved patient comfort.

Heterodyne detection enhanced by quantum correlation

Heterodyne detectors as phase-insensitive (PI) devices have found important applications in precision measurements such as space-based gravitational-wave (GW) observation. However, the output signal of a PI heterodyne detector is supposed to suffer from signal-to-noise ratio (SNR) degradation due to image band vacuum and imperfect quantum efficiency. Here we show that the SNR degradation can be overcome when the image band vacuum is quantum correlated with the input signal. We calculate the noise figure of the detector and prove the feasibility of heterodyne detection with enhanced noise performance through quantum correlation. This work should be of great interest to ongoing space-borne GW signal searching experiments.

A high signal-to-noise ratio balanced detector system for 2 μm coherent wind lidar

A balanced detector system with a high signal-to-noise ratio (SNR) is the key technology for 2 μm coherent wind lidar, which can enhance the ability for the digital receiver to detect extremely weak signals. The photodiode is the main detection component of a balanced detector system. The variance of junction capacitance of different photodiodes will cause the degradation of SNR. Based on the linear relationship between the junction capacitance of a photodiode and the reverse voltage in the double logarithmic coordinates, a balanced detector system is designed to have the ability to adjust the reverse voltage by using the external digital-to-analog converter. An optimization of the circuit performance can be achieved by adjusting the junction capacitance, which significantly affects the circuit noise and signal bandwidth in the design of the high bandwidth transimpedance amplifier, which is sensitive to parasitic capacitance and component error. A simplified optical system is built to test the performance of the designed balanced detector system. The results show that the SNR of the detector system is ∼10% higher than that of the commercial product, which can further increase the detection distance of the wind lidar by ∼1.5 km for the detection limit of 10 km.

Carrier Beating Impairment in Weakly Coupled Multicore Fiber-Based IM/DD Systems

Weakly coupled multicore fiber (WC-MCF) is promising for use in short-reach fiber telecommunication systems in the near future. Intercore crosstalk (XT) plays an important role in WC-MCF-based short-reach intensity-modulation/direct-detection (IM/DD) systems, because XT can significantly degrade system performance. For the first time, the combined effect of intercore XT and the frequency offset between optical carriers, which is defined as the carrier beating impairment (CBI), is measured and characterized by experiments and numerical simulations. The experimental results show that the CBI causes large fluctuations in the signal-to-noise ratio (SNR) with a normally tolerable XT level. Such SNR fluctuations can additionally reduce the system’s XT tolerance (at worst 1-dB SNR degradation) by as much as 20 dB for 4-level pulse amplitude modulation (PAM-4) transmission. The simulation results show that the CBI is mainly affected by the specific properties of the laser source and the modulation depth of the transmitted signals. These results suggest that the XT should be designed to be much smaller for WC-MCF-based short-reach IM/DD systems when there is the CBI.

Compressive sensing in electrical impedance tomography for breathing monitoring

Objective: Electrical impedance tomography (EIT) is a functional imaging technique in which cross-sectional images of structures are reconstructed based on boundary trans-impedance measurements. Continuous functional thorax monitoring using EIT has been extensively researched. Increasing the number of electrodes, number of planes and frame rate may improve clinical decision making. Thus, a limiting factor in high temporal resolution, 3D and fast EIT is the handling of the volume of raw impedance data produced for transmission and its subsequent storage. Owing to the periodicity (i.e. sparsity in frequency domain) of breathing and other physiological variations that may be reflected in EIT boundary measurements, data dimensionality may be reduced efficiently at the time of sampling using compressed sensing techniques. This way, a fewer number of samples may be taken. Approach: Measurements using a 32-electrode, 48-frames-per-second EIT system from 30 neonates were post-processed to simulate random demodulation acquisition method on 2000 frames (each consisting of 544 measurements) for compression ratios (CRs) ranging from 2 to 100. Sparse reconstruction was performed by solving the basis pursuit problem using SPGL1 package. The global impedance data (i.e. sum of all 544 measurements in each frame) was used in the subsequent studies. The signal to noise ratio (SNR) for the entire frequency band (0 Hz–24 Hz) and three local frequency bands were analysed. A breath detection algorithm was applied to traces and the subsequent error-rates were calculated while considering the outcome of the algorithm applied to a down-sampled and linearly interpolated version of the traces as the baseline. Main results: SNR degradation was generally proportional with CR. The mean degradation for 0 Hz–8 Hz (of interest for the target physiological variations) was below ~15 dB for all CRs. The error-rates in the outcome of the breath detection algorithm in the case of decompressed traces were lower than those associated with the corresponding down-sampled traces for CR ⩾ 25, corresponding to sub-Nyquist rate for breathing frequency. For instance, the mean error-rate associated with CR = 50 was ~60% lower than that of the corresponding down-sampled traces. Significance: To the best of our knowledge, no other study has evaluated the applicability of compressive sensing techniques on raw boundary impedance data in EIT. While further research should be directed at optimising the acquisition and decompression techniques for this application, this contribution serves as the baseline for future efforts.

A Novel Power Inversion Antenna Array for the Beidou Navigation Satellite System

Power inversion (PI) arrays have been employed to suppress interference in satellite navigation systems. When the incident direction of a satellite signal is near that of the interference, there will be a significant degradation in the signal to noise ratio (SNR). To reduce this degradation, a PI antenna array composed of a right-hand circular polarized (RHCP) antenna and a spatially-spread electromagnetic vector sensor (SS-EMVS) subarray is proposed, which can suppress interference and acquire satellite signals in both the polarized and spatial domains. Even when the satellite signal is incident from the same direction as the interference, the SNR degradation can be reduced by exploiting the difference in polarization states. It is shown that the filtering is improved in the polarization domain compared with an RHCP PI array, and the SNR loss is lower than with an SS-EMVS PI array while the computational complexity is not increased. Furthermore, the proposed PI array is effective for all Beidou satellite system public service signals.

An Investigation of the Effect of AGC Gain on the Output Signal to Noise Ratio in Cochlear Implant Sound Processing.

Measurement of speech intelligibility of cochlear implant (CI) recipients is typically carried out with a speech-innoise test procedure. Metrics which predict speech intelligibility can pre-screen new sound processing strategies prior to comprehensive testing with human subjects.The Output Signal to Noise Ratio (OSNR) metric calculates the Signal to Noise Ratio (SNR) which is present at the CI sound processor output. Watkins et al. (2018) found OSNR was an accurate predictor of speech intelligibility that could predict intelligibility in scenarios where other predictors could not.The current study investigated the effect of the sound processor automatic gain control (AGC) on OSNR and a simplified metric, Separate gain SNR (SSNR), which calculated the SNR at the CI output, assuming no interaction between the signal and noise in the sound processor. Prediction accuracy of OSNR was compared to that of Input SNR and SSNR.It was found that AGC-induced distortion and SNR degradation in speech gaps worsened OSNR. For scenarios with significant non-linear, time-varying processing, OSNR was the most accurate prediction metric. SSNR was found to be an inaccurate predictor.

MR-compatibility assessment of MADPET4: a study of interferences between an SiPM-based PET insert and a 7 T MRI system

Compromises in the design of a positron emission tomography (PET) insert for a magnetic resonance imaging (MRI) system should minimize the deterioration of image quality in both modalities, particularly when simultaneous demanding acquisitions are performed. In this work, the advantages of using individually read-out crystals with high-gain silicon photomultipliers (SiPMs) were studied with a small animal PET insert for a 7 T MRI system, in which the SiPM charge was transferred to outside the MRI scanner using coaxial cables. The interferences between the two systems were studied with three radio-frequency (RF) coil configurations. The effects of PET on the static magnetic field, flip angle distribution, RF noise, and image quality of various MRI sequences (gradient echo, spin echo, and echo planar imaging (EPI) at 1H frequency, and chemical shift imaging at 13C frequency) were investigated. The effects of fast-switching gradient fields and RF pulses on PET count rate were studied, while the PET insert and the readout electronics were not shielded. Operating the insert inside a 1H volume coil, used for RF transmission and reception, limited the MRI to T1-weighted imaging, due to coil detuning and RF attenuation, and resulted in significant PET count loss. Using a surface receive coil allowed all tested MR sequences to be used with the insert, with 45–59% signal-to-noise ratio (SNR) degradation, compared to without PET. With a 1H/13C volume coil inside the insert and shielded by a copper tube, the SNR degradation was limited to 23–30% with all tested sequences. The insert did not introduce any discernible distortions into images of two tested EPI sequences. Use of truncated sinc shaped RF excitation pulses and gradient field switching had negligible effects on PET count rate. However, PET count rate was substantially affected by high-power RF block pulses and temperature variations due to high gradient duty cycles.